Crosslinking agents or crosslinkers based on amino resins and coating compositions made with these are well known in the art and have been used for more than half a century in diverse applications including general industrial coatings, automotive coatings, coil coatings, powder coatings, baking enamels, and wood finishes. These crosslinking agents are based on reaction products of aldehydes, usually formaldehyde, with amine, amide, urethane or amidine compounds (together referred to as aminoplast formers) such as melamine, guanamines, urea, and substituted ureas. Among the major drawbacks of coatings based on these amino resins are formaldehyde emissions during cure.
Various crosslinking compositions have been developed that are based on combinations of aminoplast formers and aldehydes other than formaldehyde.
Formaldehyde free crosslinking resins for textile fabrics based on reaction products of cyclic ureas and multifunctional aldehydes having at least two aldehyde groups per molecule have been described in U.S. Pat. Nos. 4,332,586 and 4,284,758. Both US patents disclose preparation and use of alkylated glyoxal and cyclic urea condensates as crosslinkers for textile fabrics. However, the etherified adduct obtained showed a viscosity increase of about 4.6 fold upon storage for ten weeks at 48° C.
WO2012044547 and WO2012044549 describe respectively etherified and non-etherified reaction product of a cyclic urea and a multifunctional aldehyde.
WO2013142787 discloses hybrid resins or reaction products of cyclic alkylene urea with a multifunctional aldehyde and other “aminoplast formers”. Examples of such aminoplast formers include linear and cyclic urea derivatives, amines, acid amine, urethanes, amino functional triazine derivatives, etc.
U.S. Pat. No. 8,133,952 describes the use of cyclic urea as a blocking agent of a product based on a use of polyvinylalcohol and a polyaldehyde crosslinker. This patent refers to a formaldehyde free curable aqueous composition for use as binder for non-woven products which requires the presence of a high molecular weight polyvinyl alcohol.
U.S. Pat. No. 4,625,029 discloses cyclic urea/glyoxal/polyol condensates for use as formaldehyde free crosslinking agent resins for cellulosic textile fabrics. The polyols used are for example ethylene glycol, diethylene glycol and the like.
However, despite numerous efforts made, there is still a need to develop formaldehyde free crosslinking compositions based on reaction products of cyclic alkyleneureas and multifunctional aldehydes which show satisfying properties especially with regard to the shelf stability and the heat-aged film color stability when using in coating composition.